Interpretive Summary: Vegetable growers are losing the broad-spectrum soil fumigant methyl bromide. Significant research effort is on-going to develop weed control alternatives to methyl bromide in vegetable crop production. Research on alternatives to methyl bromide fumigation in Georgia began in the early 1990's. In preliminary trials, methyl bromide was not a consistent performer in controlling yellow nutsedge and Vapam HL applied as a spray and incorporated was among the most effective fumigants for controlling yellow nutsedge. However, there are many unanswered questions about using Vapam HL for weed control. Irrigated field trials were conducted in 2001 and 2002 at Tifton, GA on transplanted cantaloupe to evaluate weed control using all possible combinations of three rates of Vapam HL, three preplant fumigation intervals, and two levels of plastic mulching. Preliminary results indicated that fumigation 2-wk before transplanting provided the best combination of yellow nutsedge control and protection from fumigant phytotoxicity of the preplant intervals evaluated. Fumigation 1-wk before transplanting provided the most effective yellow nutsedge control, but stunted cantaloupe and slightly delayed maturity. Vapam HL fumigation 3-wk before transplanting was not as effective in controlling yellow nutsedge as fumigation closer to transplanting and yields were reduced by weeds. Plastic mulch improved yellow nutsedge control and increased cantaloupe yield. Plots fumigated with the full-rate of Vapam HL had the most effective yellow nutsedge control and greatest yields compared to either nonfumigated or treated with a reduced rate of Vapam HL. The yield response is due to superior yellow nutsedge control provided by the full-rate. These preliminary results suggest that Vapam HL use patterns can be modified to make it an attractive, cost-effective alternative to methyl bromide for weed control. These modified Vapam HL application techniques can be easily implemented by vegetable crop growers when methyl bromide can no longer be used.

Technical Abstract:
Irrigated field trials were conducted in 2001 and 2002 at Tifton, GA on transplanted cantaloupe to evaluate weed control using all possible combinations of three metham-sodium rates, three preplant fumigation intervals, and two levels of plastic mulching. Preliminary results indicated that preplant metham-sodium fumigation 2-wk before transplanting provided the best combination of yellow nutsedge control and protection from fumigant phytotoxicity of the preplant intervals evaluated. Fumigation with metham-sodium 1-wk before transplanting provided the most effective yellow nutsedge control, but the fumigant applied just prior to transplanting stunted cantaloupe and slightly delayed maturity. Metham-sodium fumigation 3-wk before transplanting was not as effective in controlling yellow nutsedge as fumigation closer to transplanting and yields were correspondingly lower due to nutsedge interference. Plastic mulch improved yellow nutsedge control and increased yields in all possible combinations of fumigant rates and times of preplant fumigation. Plots fumigated with the full-rate of metham-sodium had the most effective yellow nutsedge control and greatest yields compared to either nonfumigated or treated with metham-sodium at the 2x rate. The yield response is due to superior yellow nutsedge control provided by the full-rate. These preliminary results suggest that metham-sodium use patterns can be modified to make it a more attractive cost-effective alternative to methyl bromide than originally thought.